Automated Growing Rod Device

ABSTRACT

A remotely controllable growing rod device comprises a housing containing on-board electronics and at least one drive assembly operable to move associated extension elements relative to each other. Each extension element terminates in an anchor element configured to be anchored to a part of the spine, such as the pedicle of a vertebral body. The on-board electronics includes a microprocessor, a power supply, such as an inductive power supply, and a receiver/transmitter. The microprocessor is configured to receive remotely transmitted movement data through the receiver and is further configured for feedback controlled actuation of the drive assembly for relative movement the associated extension elements to achieve a desired physiological condition of the patient&#39;s spine.

PRIORITY CLAIM

This application is a continuation of and claims priority to co-pendingutility patent application Ser. No. 13/072,684, filed on Mar. 26, 2011,which issued on Nov. 19, 2013, as U.S. Pat. No. 8,585,740, and which isa continuation-in-part and claims priority to co-pending utility patentapplication Ser. No. 13/004,752, filed on Jan. 11, 2011, now abandoned,the entire disclosure of which is incorporated herein by reference,which application claims priority to provisional application No.61/294,444, filed on Jan. 12, 2010, now expired, the entire disclosureof which is incorporated herein by reference.

BACKGROUND

The present invention relates to a “growing rod” device, namely a devicethat is adapted to be mounted to a long bone or to the spine of apatient and that incorporates the ability to have its overall lengthextended (distracted) or reduced (compressed) in situ.

Growing rod devices have been developed for implantation in the spine ofa child to correct an abnormal curvature of the spine, such asscoliosis. In devices of this type, a rod assembly is progressivelylengthened to reduce the abnormal curvature while allowing the child'sbody to adapt to the revised spinal position. One typical growing roddevice includes of a pair of axially aligned rods, each terminating inan anchor element configured for attachment to the spine. Lengthening ofone or both rods requires a surgical procedure to advance the effectiverod lengths, usually about every six months. This approach requiresmultiple surgeries, often over a multi-year period, with the resultbeing the correction of the spine curvature caused by the onset ofscoliosis.

While growing rod devices have demonstrated their value in correctingserious spinal deformities, the need for multiple surgeries is highlyproblematic. There is a significant need for a growing rod device thatdoes not require surgical intervention to adjust the length of thedevice.

SUMMARY

In accordance with one feature, the present invention provides a growingrod device that may be remotely controlled while implanted within thepatient, thereby eliminating the need for separate surgical proceduresto adjust the length of the device. In one embodiment, the devicecomprises a housing containing on-board electronics and supporting driveassemblies operable to extend or retract associated extension elementsprojecting along the axis of the device. Each extension elementterminates in an anchor element configured to be anchored to a part ofthe anatomy, such as the pedicle of a vertebral body or to a long bone.Each drive assembly includes a micromotor and a threaded interfacebetween the motor and the corresponding extension element. In oneembodiment a drive rotor is rotatably disposed within a stator that isfixed to the housing. The threaded interface between the drive rotor andthe extension element converts rotation of the rotor to translation ofthe extension element for extension/distraction or compression of thespine or bony anatomy.

In a further aspect, the on-board electronics includes a microprocessor,a power supply and a receiver/transmitter. In one aspect the powersupply is an inductive power supply that relies upon inductive energytransmission from an external device. The power supply may include arechargeable battery that is inductively charged or may constitute apower converter that provides electrical power to the on-boardelectronics only when energized by the external inductive power source.

In another aspect, the on-board electronics of multiple growing roddevices implanted within a patient may communicate via a common databus. The microprocessor of each such device has a unique address oridentifier so that only control signals pertinent to the particulardevice are transmitted to or acknowledged by that device. The on-boardelectronics may also incorporate various condition sensors, such asrotation and translation sensors operable to determine movement of thedrive assembly components, strain gages operable to transmit load data,and temperature sensors, for example.

A handheld programming unit is provided in another aspect of theinvention. The handheld unit provides an external interface to theimplanted growing rod device(s), in particular to communicate movementdata to the devices and to receive data transmitted by the devices. Thehandheld unit interfaces with software, resident on the unit or in aseparate computer, which permits generation of movement data for eachgrowing rod device in a patient. On the handheld unit movement data maybe directly input via a keypad. Alternatively or in addition, softwaremay be provided that calculates movement data or a movement protocol.The software may incorporate GUI interface for interaction with thecaregiver or caregiver/surgeon to generate the movement data orprotocol. This movement information may be uploaded to the handheld unitor in some cases communicated directly to the implanted device.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a depiction of a growing rod device according to the presentinvention mounted to the spine of a patient.

FIG. 2 is an exploded view of a growing rod device according to oneembodiment of the invention.

FIG. 3 is an exploded view of a growing rod device according to afurther embodiment of the invention.

FIG. 4 is a side cross-sectional view of the growing rod device shown inFIG. 3.

FIG. 5 is a block diagram of the on-board electronics of a growing roddevice according to embodiments of the present invention.

FIG. 6 is an enlarged cross-sectional view of a locking mechanism forlocking the extension elements of the growing rod devices disclosedherein.

FIG. 7 is a plan view of a programming unit for use in controllingactuation of the growing rod devices in one embodiment.

FIGS. 8-10 are screen shots of a GUI for a software program used togenerate movement data or a movement protocol for growing rod device(s)implanted within a patient.

FIG. 11 is an end perspective view of a manual adjustment feature of thegrowing rod device shown in FIG. 2.

FIG. 12 is a flowchart of a software program executed by a growing roddevice in an autonomous adjustment mode of operation.

FIG. 13 is a block diagram of a controller for controlling operation ofthe growing rod devices disclosed herein.

DETAILED DESCRIPTION

According to one embodiment, an automated growing rod device 10 includesa main housing 12 and two drive assemblies 14, 15 attached to oppositeends of the main housing, as shown in FIGS. 1-2. Extension elements 16,17 project from opposite ends of the device, and may be coaxiallyaligned. The end of each extension element terminates in an anchorelement 18, which may be a slotted plate, as shown in FIGS. 1-2, or anelongated rod, as shown in FIG. 3. In the embodiment shown in FIG. 1,the anchor elements 18 are fastened to a vertebral body V1, V3 byappropriate bone engaging fasteners, such as bone screws or bone bolts,with the device spanning the intermediate vertebra V2. It is understoodthat other bone engaging fasteners may be employed to engage anelongated rod anchor element to the spine.

As shown in FIG. 1, the growing rod assembly spans several vertebrallevels, three in the illustrated embodiment. As explained herein, thegrowing rod device operates to drive the extension elements 16, 17apart, lengthening the device 10 and thereby changing the angle of spine(i.e., the Cobb angle) at the instrumented levels, with the ultimategoal being to straighten the spine as much as possible.

In one embodiment, a growing rod device 10 includes extension elements16, 17 in the form of elongated rods terminating at one end in theanchor element 18 and having a threaded shank 16 a, 17 a at the oppositeend. The threaded shanks of the two extension elements are containedwithin the cavity 30 defined in the main housing 12. Each threaded shankis configured to engage an internally threaded bore 20 a, 21 a of acorresponding drive rotor 20, 21, as best seen in FIG. 2. The driverotors 20, 21 form part of the drive assemblies 14, 15. The driveassemblies further include stator elements 22, 23 that operate to rotatethe drive rotors when the drive assemblies 14, 15 are energized. Thedrive assemblies are mounted or fastened to the main housing 12 so thatthe stator elements remain fixed and non-rotating within the growing rodassembly 10. It can be appreciated that the stator elements andcorresponding drive rotors are constructed as a conventionalelectromagnetic motor so that activation of the stator elements resultsin rotation of the drive rotors. As the drive rotor 20 rotates, theinterface between the threaded bore 20 a and the threaded shank 16 aleads to translation of the extension element 16. Rotation of the driverotor in one direction causes the extension element to extend away fromthe main housing 12, while an opposite rotation causes the extensionelement to retract within the housing. It can be appreciated that thestator 23, drive rotor 21 and threaded shank 17 a work in the same wayto extend or retract the opposite extension element 17.

The thread pitch of the threaded shanks 16 a, 17 a and rotor threadedbores 20 a, 21 a is preferably sized to permit finely tuned lengtheningof the device. In addition, the thread pitch can help provide amechanical advantage to provide the distraction force necessary to pushinstrumented vertebrae against the normal spinal loads. In certainprocedures, the distraction force necessary for effective correction ofa spinal deformity is at least 20 lbf. Distraction forces up to 45 lbfmay be suitable for certain procedures. In a specific embodiment, thedrive assemblies are capable of generating a torque of 40-50 in-ozs toachieve the required distraction force. In a specific embodiment, thethreads of the extension elements and drive rotors may have a pitch of40-50 tpi and a thread angle of about 2.5°. The thread angle may bepreferably selected to minimize the torque generated by the driveassemblies, particularly since that torque must be reacted by thepatient's anatomy. The extension elements may be formed of stainlesssteel, titanium, cobalt-chrome or other suitable medical grade materialcapable of withstanding the significant spinal loads without measurablebending or twisting. The extension elements may have a diameter of 0.5in, or other diameters consistent with spinal implants. If the growingrod device 10 is used in other settings, such as for long bonelengthening, the extension elements may be appropriately sized.

In order to ensure that the extension elements only translate and do notrotate, an anti-rotation feature is incorporated into the driveassemblies and threaded shanks. In one embodiment, the drive assemblies14, 15 include a corresponding anti-rotation washer 25, 26 interposedbetween the drive assemblies and the main housing 12. The washersinclude an inwardly projecting tang 27 that is configured to slidablyfit within a groove 28, 29 in the threaded shanks 16 a, 17 a. Since thewashers 25, 26 are fixed to the housing, the tangs 27 cannot rotate, andsince the tangs are received within the grooves 28, 29 the extensionelements 16, 17 cannot rotate. The tangs and grooves are sized to permitfree relative sliding movement between the components, but aresufficiently tightly toleranced so that the amount ofextension/retraction (or the overall length) of the growing rod assembly10 can be precisely known. In other words, too much slop between thetang and groove can permit a small amount of angular movement of theextension element which translates to a slight change in axial positionof the extension element.

Another embodiment is shown in FIGS. 3-4 in which a growing rod assembly10′ includes telescoping extension elements. The assembly 10′ includesan extension element 17′ having an elongated rod for the anchor element18′ and a hollow threaded shank 17 a′ at the opposite end. The hollowthreaded shank 17 a′ defines an elongated cavity 19′ that is sized toreceive the threaded shank 16 a′ of the opposite extension element 16′,as best shown in FIG. 4. This telescoping or overlapping feature allowsthe growing rod assembly 10′ to have the same stroke or throw as theassembly 10 shown in FIG. 2, but in a smaller envelop. In the embodimentof FIG. 2, the two extension elements 14, 15 abut inside the mainhousing 12 when the extension elements are in their fully retractedposition. On the other hand, when the extension elements 16′, 17′ ofFIG. 4 are fully retracted the threaded shank 16 a′ of extension element16′ is positioned entirely within the cavity 19′ of the other extensionelement. This feature allows the growing rod assembly 10′ to have afully retracted overall length that is less than the overall length ofthe assembly 10 by the length of the cavity 19′. This retracted lengthdifference may permit the use of a smaller main housing 12′ in theembodiment of FIGS. 3-4 over the other embodiment. More importantly,this overlap or telescoping feature allows the device to have asignificantly smaller length when the device is being initiallyimplanted within the patient. The smaller envelop simplifies the surgeryand reduces the overall trauma to the patient when the device isimplanted.

As illustrated in FIG. 3, the drive rotor 21′ for the extension element17′ has a larger diameter than the drive rotor 20′. The drive rotors 20′and 21′ are sized to receive the threaded shanks 16 a′ and 17 a′threaded into the threaded bores 20 a′, 21 a′. Thus, since the shank 16a′ extends into the shank 17 a′ this latter shank is necessarily of alarger diameter, which thus requires a larger diameter drive rotor. Thedrive assembly 15 may be appropriately sized to accommodate the largerdrive rotor 21′. Thus, the drive assembly 15′ and stator 23′ may belarger in profile than the opposite drive assembly 14′ and stator 22′.Likewise, the anti-rotation washers 25′ and 26′ are sized to receive thecorresponding threaded shank 16 a′, 17 a′.

Returning to FIG. 2, the main housing 12 of the growing rod device 10(as well as the housing 12′ of the device 10′) includes an electronicshousing 32. This housing contains the on-board electronics necessary topower and control the growing rod device 10/10′ remotely. It iscontemplated that the growing rod devices of the present invention arewholly self-contained, meaning that no physical external connections arerequired, such as a physical connection to an external power source orcontrol unit. Consequently, in one embodiment, the electronics housing32 contains on-board electronics as depicted in FIG. 5. This electronicsincludes a microprocessor 52 with an associated power supply 53. Thepower supply is capable of powering all of the on-board electronics aswell as the drive motor assemblies. In one embodiment, the power supplyis a battery pack of several small “watch” batteries. Alternatively, thebattery pack may include one or more rechargeable batteries that can beinductively charged while remaining in situ within the patient. Forinstance, the power supply 53 may constitute a 7.4V Ni—Cd batterycapable of holding a charge for about 30 minutes. In another embodimentthe power supply is a lithium poly battery. In yet another alternative,the power supply may be an inductive power supply that is only energizedwhen inductively (but not physically) coupled to an external device. Theinductive power source may be incorporated into the patient table sothat the power supply 53 is only capable of being energized or poweredwhen the patient is resting on the table. This approach can eliminatethe need for a power supply in the on-board electronics for the device10. However, in some cases it may be desirable to maintain a small powersupply or battery for the microprocessor, particularly when separatesensors are to be monitored.

The on-board electronics also includes a signal receiver 54 that issmall enough to be contained within the small envelop of the electronicshousing 32 but capable of receiving and transmitting a signal fromwithin the patient. The receiver 54 may also incorporate transmitterfunctions to transmit information regarding the health of the growingrod device or to transmit data obtained from associated sensors. Forinstance, in some cases it may be desirable to include a temperaturesensor within the main housing 12 to monitor the temperature of thedevice as it is being operated to translate the extension elements. Inaddition, the device may include a strain gage that monitors the strainexperienced by the extension elements 16, 17 under load. The signalreceiver 54 may be configured to transmit and receive RF signal. It isfurther contemplated that a pair of encoders may be provided thatmeasure the amount and rate of rotation of each drive assembly 20, 21.For instance, encoders disposed within the electronics housing 32 may bearranged to respond to passage of openings 66 defined in a flange 67 ofeach drive rotor, such as depicted in FIG. 6.

The on-board electronics includes a microprocessor 52 that providescontrol signals to various motor controllers based on remotelytransmitted data received by the receiver 54. The microprocessor isconfigured to translate the remotely transmitted movement data tocommand signals to a motor controller 55 coupled to the stator 22 of thedrive assembly 14, and to a motor controller 56 coupled to the stator 23of the other drive assembly 15. The motor controllers 55, 56 andassociated stators may be capable of bi-directional movement, or bothclockwise and counter-clockwise rotation. Alternatively, a second set ofstators may be provided in each drive assembly, with one statorresponsible for clockwise rotation and the other responsible forcounter-clockwise movement. In this case, additional motor controllersmay be provided.

The drive assemblies 14, 15 may incorporate features that permit manualadjustment of the growing rod without activation of the motorcontrollers 55 and 56. Thus, referring to FIG. 11, the ends of the driveassemblies may be configured as a driving nut 20B, 21B (FIG. 2) that canbe engaged by a tool, such as wrench 70, to manually rotate thecorresponding drive assembly. Rotation of the drive assembly 14, 15causes translation of the corresponding extension element 16, 17 asdescribed above.

In order to ensure that the device does not collapse or extendinadvertently, the device may include a locking solenoid 65 mountedwithin each drive assembly, such as the drive assembly 15 shown in FIG.6. The plunger of the solenoid is sized to be received within one of aplurality of openings 66 circumferentially spaced around acircumferential flange 67 of the drive rotor 21 (see FIG. 2). Thesolenoid may be configured so that the plunger is extended in thede-energized state of the solenoid. When it is desired to change thelength of the device 10, the solenoid 65 is energized by themicroprocessor (FIG. 5) and the plunger retracts free of the opening inthe drive rotor, thereby permitting rotation of the rotor. Themicroprocessor may be configured to automatically extend the plunger atthe end of a movement cycle and automatically retract the plunger at thebeginning of the movement.

In a specific embodiment, for a growing rod device capable of spanningthree or more vertebral motion segments, the main housing and driveassemblies may have a combined overall length of less than 50 mm. Theextension elements may be rods each having a total length of about 60mm. For the device 10 shown in FIG. 2, the overall retracted length ofthe device would be about equal to the combined length of the twoextension elements, or about 120 mm. It is contemplated that eachextension elements may be extended about 15 mm, leaving about 10 mm ofthe extension element disposed within the corresponding drive assembly,for a total extended length of about 150 mm. For the device 10′ shown inFIG. 3, the extended length would be the same but the retracted lengthwould be much less due to the telescoping or overlapping feature of thisembodiment. In one specific embodiment the two extension elements 16′,17′ may be configured for an overlap of about 20 mm, thereby reducingthe overall retracted length of the device to about 100 mm.

The main housing and drive assemblies are formed of a medical gradematerial that is sufficiently strong to react the load from lengtheningthe extension elements. In one specific embodiment the main housing anddrive assemblies are formed of a polymeric material, such as PEEK resinfor the drive rotors and LP resin for the stator and main housing.

In most procedures for correction of spinal deformities, a growing roddevice is implanted on either side of the spine. Thus, in the case of ascoliotic spine, a growing rod device is placed to distract the concaveside of the spinal curve, or open up the concavity, while a device onthe opposite convex side of the scoliotic curvature compresses thespine. The combination of the two motions ensures that the spinederotates uniformly without any lateral movement of the vertebrae. Thismulti-axis correction also prevents rotation of the spine about itsaxis. It can thus be appreciated that a typical spinal correctionconstruct will include two growing rod devices, such as device 10 withfour total extension elements 16, 17, two on each side of the spine. Thetask facing the caregiver/caregiver/surgeon is to provide a coordinatedplan for optimum extension or retraction of the four extension elementsto correct the bad curvature without introducing any other deformityconditions.

In certain embodiments it is contemplated that the multiple growing roddevices implanted within the patient are in communication, such as by adata bus coupled between the microprocessors 52 of the devices. In thisinstance, external communication with the devices can be limited to oneprimary microprocessor. The microprocessor of each device has a uniqueaddress. Software within the primary microprocessor, such as within ahandheld programming unit 100 discussed below, can be configured to sendcontrol signals specific to each device and to identify transmitted dataas associated with a corresponding device. This feature allows the useof multiple devices within a patient to provide multi-axis correction ofthe patient's spine. For instance, two devices fastened to pedicles oftwo vertebrae may provide correction of a scoliotic curvature in thesagittal plane, while another growing rod device fastened to a lateralsurface of two vertebral bodies may provide correction of a complexcurvature in the AP plane. All three growing rod devices would have aunique address. All data transmission would occur with the primarymicroprocessor that would then communicate with the specificallyaddressed growing rod device over the common data bus. As shown in FIG.5, the microprocessor 52 may communicate with four motor controllers—themotor controllers 55, 56 discussed above associated with a growing roddevice on one side of the spine, and motor controllers 60, 61 associatedwith a growing rod device on the opposite side of the spine. It isunderstood that the microprocessor 52 in FIG. 5 may represent a singlemicroprocessor charged with controlling the four motor controllers 55,56, 60, 61, or the microprocessor in the figure may be a representationof the separate individual microprocessors associated with each growingrod device. In the latter case, each microprocessor would beindividually uniquely addressed, as described above.

The growing rod device 10 of the present invention contemplates ahand-held programming unit, 100 such as shown in FIG. 7. The programmingunit includes a microprocessor and a receiver/transmitter configured forcommunication with the receiver/transmitter 54 of the device 10. Thehand-held unit 100 may be configured to dock with a computer to up-loada distraction protocol and download data that may be obtained from thegrowing rod device 10. Alternatively, the unit 100 may be used toindependently program each threaded rod “delta”—that is the desiredextension/retraction or linear movement for each extension element.After each rod position is programmed by the physician, thepre-determined program is actuated by placing the remote programmingunit in an execute mode and simultaneously pressing two “execute”buttons or keys on the programming unit coupled with the three positiondead man switches. If either of the two buttons is released, theexecution is halted.

In the embodiment depicted in FIG. 7, the unit 100 is configured toprogram and actuate four extension elements, with each element having aseparate set of indicators 101. Each extension element can besuccessively selected by the caregiver/caregiver/surgeon to program thecorresponding element. A green LED may be illuminated when a particulardevice is being programmed. A keypad 103 allows the caregiver/surgeon todirectly input a specific delta for the given extension element. Whenall of the devices have been programmed the drive assembly for eachextension element may be actuated by entering the “execute” mode of theprogramming unit 100. In order to prevent accidental activation, a pairof “execute” buttons must be depressed simultaneously and held depressedduring the actuation cycle. Red LEDs and a pair of “servo moving” and“execute mode” indicators are illuminated to verify that the growing roddevices are in operation to increase or decrease their respectivelengths. The activation of the devices can be terminated by releasingone or both of the “execute” buttons, or when the pre-programmed deltahas been achieved for each drive assembly and extension element.

In certain embodiments the programming unit 100 is maintained by thecaregiver/surgeon/physician. The unit 100 may interface with a computersystem that includes software for generating an adjustment protocol forthe particular patient. The software can accept data regarding thenature and extent of the spinal deformity, such as digitized dataindicative of the position and orientation of vertebral landmarks. Acomparison of the deformity data to an idealized spinal position for theparticular patient can be used to determine the form and extent ofmovement of the spine necessary to approximate the ideal spinalposition. This desired movement information can provide the basis fordetermining the incremental movements made over time, ultimatelyresulting in delta data for each extension element of each growing roddevice. This movement protocol may thus be generated by software in thecomputer system, or alternatively may be determined separately by thecaregiver/surgeon. This movement protocol can then be uploaded to thehandheld programming unit 100.

It is further contemplated that in certain embodiments the programmingunit 100 may be kept by the patient or a local care-giver. The unit 100may be remotely programmed with movement data, such as via an Internetinterface or a wireless transmission. Once the movement data is uploadedto the programming unit, the patient or local care-giver can activatethe unit to effect movement of the growing rod devices implanted in thepatient. In this instance, the programming unit 100 may include aninductive power source to provide power the power supply 53 of thegrowing rod device(s), as explained above. The patient-associatedprogramming unit may be modified from the unit described above toeliminate the programming capabilities and to incorporate securityfeatures that disable the unit unless and until movement data has beentransmitted to the unit.

In certain embodiments, the computer program used to program the growingrod device movements may incorporate a graphical user interface thatguides the caregiver/surgeon through the movement generation process.Exemplary GUI screens are shown in FIGS. 8-10. The initial screen ofFIG. 8 allows the caregiver/surgeon to select the location of thegrowing rod devices, whether in the upper or lower back, since themovement protocols will vary depending upon whether the movement is inthe lumbar or thoracic spine. The initial screen may also allow thecaregiver/surgeon to establish the manner of communication of themovement protocol to the hand-held unit 100. Another GUI screen shown inFIG. 9 establishes communication with the unit 100, whether it ismaintained by the caregiver/surgeon or the patient.

An exemplary GUI for programming the growing rod device movements isshown in FIG. 10. Once a particular vertebral level has been selected(in cases in which more than one pair of devices is utilized) thecaregiver/surgeon can input a desired movement delta for either side ofthe spine. A specific entry may be made indicating whether the delta isextending or expanding the growing rod device for distraction of thespine, or compressing/retracting the device for compressing the spine.The GUI may provide means for uploading the pre-programmed movementprotocol to the hand-held unit 100, or may directly interface with thegrowing rod devices themselves to execute the movement protocol. It isfurther contemplated that the software will maintain a database of thedata transmitted to and from the implanted growing rod devices.

The GUI and associated software may be resident on a local computer ormay be incorporated into the handheld programming device 100 with anappropriate modification to include a display screen. The software mayalso be implemented as an application for a more sophisticatedcommunication device or mobile phone.

The handheld unit 100 has the capability for remote communication withthe implanted growing rod device(s), including not only sending movementdata but also receiving status information from the device(s). Themicroprocessor 52 of each growing rod device generates information as tothe status of the on-board electronics as well as the drive assemblies.Fault conditions may be sensed by the microprocessor and an appropriatewarning transmitted to the handheld unit 100. For instance, the on-boardelectronics may incorporate means for detecting the rotation of thedrive rotors 20, 21 and the linear movement of the extension elements16, 17. Real-time movement data may be transmitted to the handheld unitto provide a visual indication to the caregiver/surgeon. Lack ofmovement or a discrepancy between rotation of a rotor and linearmovement of a corresponding extension element can generate an errorsignal that is transmitted to the handheld unit. As indicated above,strain gages may be associated with the extension elements to indicateloading as the device is expanded and to provide a warning if apre-determined strain value is exceeded. Temperature sensors cantransmit temperature data to the handheld unit through the on-boardmicroprocessor.

In a further feature, the microprocessor 52 for each growing rod device10 executes program steps for coordinated movement of the extensionelements 16, 17. In a first step for using the device the surgeon ormedical advisor determines the amount of lengthening or compression thatshould occur at the instrumented bone or spinal segment. These lineardimensions are communicated to the microprocessor for the affectedgrowing rod device, preferably via the handheld unit 100. Themicroprocessor then calculates the appropriate amount of rotation of thedrive motor assemblies to produce a linear displacement of the extensionmembers to meet the requested lengthening or compression. In theillustrated embodiments, two drive assemblies 14, 15 produce therequested extension/compression which means that the two drive rotors20, 21 are rotated. The microprocessor implements software thatcoordinates the movement of the two drive rotors so that the rotors arerotated at the same time. It can be appreciated that simultaneousrotation eliminates any torque concerns since an opposite torque will beapplied to the two rotors by their respective drive assemblies.Moreover, it can be appreciated that the simultaneous coordinatedmovement of the drive rotors, and consequently the simultaneouscoordinated extension/retraction of the extension members 16, 17produces the requested movement with as little stress to the patient aspossible. It is further contemplated that the microprocessor 52 isoperable to move the drive rotors in opposite axial senses—i.e., one maymove in compression while the other moves in distraction.

As the drive assemblies rotate the respective rotors, the amount ofrotation is monitored, such as by using the encoder described above. Themicroprocessor 52 may evaluate the encoder signals to determine not onlythe amount of rotation but the rate of rotation. The microprocessor canthen implement a feedback process that maintains coordinated movement ofthe rotors. Thus, if one rotor is rotating more quickly than the otherrotor, the microprocessor can issue a control command to one driveassembly to either speed it up or slow it down, as appropriate forcontrolled extension/retraction. The microprocessor also evaluates theencoder signals to determine whether the movement is complete, at whichtime it de-energizes the drive assemblies to stop the growing roddevice. At the same time the microprocessor may activate the lockingsolenoid 65 discussed above to lock the respective drive rotors. It is,of course, contemplated that the threads between the drive rotors andthe extension elements may be configured to effectively lock theextension elements in their final position, without the need for aseparate locking solenoid.

The microprocessor 52 and handheld controller 100 may include softwarethat provides controlled coordinated movement of multiple growing roddevices. As discussed above, treatment of severe spinal deformities,such as scoliosis, often require movement of different spinal segmentsin different ways. In some procedures, two pairs of growing rod devicesmay be implanted in a patient—one pair on opposite sides of the midlineat the lumbar spine and another pair on opposite sides of the midline atthe thoracic spine. It can be appreciated that while the growing rod onone side of the midline must be extended to correct an improper lateralcurvature of the spine, the other growing rod on the opposite side ofthe midline must retract or shorten. It can also be appreciated thatcorrection of curvature in the lumbar spine will necessarily affect thethoracic spine. Consequently, coordinated simultaneous movement in bothspinal levels may be desirable to provide accurate correction with aslittle stress to the patient and the patient's spine as possible.

As explained above, the handheld unit 100 is capable of communicatingwith multiple growing rod devices, each device having a unique addressfor wireless communication. More particularly, the microprocessor 52associated with each growing rod device maintains the unique address sothat the microprocessor only responds to signals received by thereceiver 54 that carry that unique address. Thus, when the surgeonenters the adjustment data on the handheld unit the adjustment data iscommunicated to the associated growing rod device 10. When the surgeonactivates the adjustment process (by depressing the two “execute”buttons) the handheld unit transmits an execute signal that issimultaneously received by all the growing rod devices and each suchdevice immediately begins moving their associated extension elements 16,17. The microprocessor of each growing rod device returns signals to thehandheld unit that identifies the particular device and indicate thestatus of the extension element movement. If communication between thehandheld unit and any one of the growing rod devices is interrupted thehandheld unit transmits a stop command to each device so that furthermotion ceases. If any growing rod device begins to move out of sync withthe other devices, the handheld unit may again issue a stop command toall devices. Alternatively, the microprocessor of the handheld unit maybe programmed to issue device specific commands to adjust the extensionor retraction of the particular device or devices as necessary torestore the coordinated motion among all of the growing rod devices.

The present invention further contemplates growing rod devices capableof autonomous adjustment. More specifically, the on-board microprocessor52 for a growing rod device may execute software that follows anextension/retraction protocol that may be pre-programmed by the surgeonusing the handheld unit 100. The microprocessor includes an embeddedclock or timer that can be initiated when the growing rod device isinitially implanted and the autonomous adjustment sequence is activatedby the surgeon. The software in the on-board processor may executesoftware according to the flowchart shown in FIG. 12. Once theautonomous adjustment sequence is initiated the microprocessor goes into“sleep mode” where the microprocessor and device are inactive, exceptfor various monitoring or self-monitoring functions. Examples of thesemonitoring functions may include the state of the on-board power supply,device temperature (which may be indicative of a physical problem withthe patient), orientation of the bone segments or spine, or a change inposition of the extension elements 16, 17.

During the sleep mode the microprocessor on-board clock or timerdetermines whether a pre-determined period has passed, such as one monthin the example of FIG. 12. This time period is established by thesurgeon based on the treatment protocol. For instance, in treatingscoliosis the patient's spine is typically adjusted every month. Thistime period may be adjusted by the surgeon as appropriate for thepatient and treatment protocol. In one embodiment, once the requisitetime has passed, the microprocessor may determine whether the currenttime is at night, since it is likely that the patient is inactive andrelaxed. This determination may be made by referring to an on-boardreal-time clock, although wireless access to a remote clock via thetransmitter/receiver of the on-board electronics is contemplated. If thecurrent time is not at night the device returns to the sleep mode untila nighttime condition is sensed. If the appropriate time is met, thenthe routine implement by the microprocessor 52 determines whether thepatient is lying down, since the requisite length adjustments may onlybe made when the patient is reclined, particular for spinal adjustments.This determination may be made using body position sensors integratedinto the growing rod device or carried by the patient.

Once all the pre-conditions have been met, the microprocessor maycommand the drive assemblies to move the extension elements 16, 17according to the pre-programmed length adjustment protocol. In oneembodiment, the movement only occurs according to the pre-programmedprotocol. Alternatively, the length adjustment may be based on strainreadings of the extension elements. In this embodiment, each extensionelement 16, 17 is outfitted with a strain gage or a series of straingages along the length of the element. When the microprocessordetermines that it is time for a length adjustment of the growing roddevice, the microprocessor polls the strain gages for the extensionelements. As reflected in the last steps of the flowchart in FIG. 12,the goal of monitoring the strain gage values is to produce a movementthat produces an essentially zero strain state within the extensionelement. Thus, if the measured strain for a particular element isnegative, the element is adjusted to contract, while if the measuredstrain is positive the extension element is extended or expanded. It iscontemplated that only slight pre-determined adjustments are made andthe microprocessor program loops until the accumulated adjustments haveachieved the desired zero strain state. (It can be appreciated that themeasured strain need not be exactly zero but may fall within apre-determined range). Once the necessary length adjustments have beenmade the microprocessor returns to the sleep mode.

The software steps implemented by the microprocessor may be modifiedspecifically for the treatment of spinal deformities, such as scoliosis.In a scoliosis condition, the patient's spine is abnormally curved inthe lateral plane of the patient—i.e., from side to side. The abnormallycurved portions of the spine, such as the lumbar or thoracic spine,subtend an angle known as the Cobb angle. The goal in the treatment ofscoliosis is to reduce the Cobb angle to as close to zero as possible,which corresponds to a perfectly straight spine. In practice, however,it is usually not possible to achieve a zero Cobb angle, so mosttreatments are directed to a satisfactory ending angle, such as 7-10degrees. In the modification reflected in the flowchart of FIG. 12, themicroprocessor may determine the Cobb angle for the patient. The Cobbangle may be determined using strain gage data from the extensionelements or position sensors associated with the growing rod device orthe patient. For instance, fiducials may be associated with the ends ofthe extension elements or with particular vertebrae of the patient. Themicroprocessor evaluates the sensor data to calculate the Cobb angle atthe particular moment in time. If the Cobb angle is within apredetermined range for the particular moment in time (i.e., is the Cobbangle satisfied) then no length adjustment is required and the devicereturns to the sleep mode. On the other hand, if the Cobb angle isoutside the desired range, the microprocessor proceeds with thesubsequent steps to adjust the growing rod length as described above.

In accordance with one embodiment, the microprocessor 52 for the growingrod system may follow the architecture shown in the block diagram ofFIG. 13. The microprocessor may receive input signals from an embeddedclock 80 and real-time strain sensors 82 as discussed above. Additionalinput signals may be received from real time force sensors 84 associatedwith the device that measure the force generated by or against theextension elements. Body position sensors 86 may also provide inputsignals to indicate, for instance, whether the patient is reclined. Themicroprocessor can incorporate a PID controller that implements expertfuzzy logic to determine the proper movement of the extension elementsto achieve an ideal spine correction.

While the invention has been illustrated and described in detail in thedrawings and foregoing description, the same should be considered asillustrative and not restrictive in character. It is understood thatonly the preferred embodiments have been presented and that all changes,modifications and further applications that come within the spirit ofthe invention are desired to be protected. For instance, the presentdisclosure relates to the compression/distraction of the spine tocorrect an abnormal curvature or deformity. The automated growing roddevices disclosed herein may also be utilized to increase the length ofa long bone or to assist in fracture fixation and compression.

What is claimed is:
 1. A growing rod device for implantation in apatient comprising: a pair of elongated extension elements, eachextension element including an anchor element at an anchor end thereofconfigured to be anchored to a portion of a patient's spinal anatomy andeach including an opposite end opposite said anchor end, a driveassembly coupled to said opposite end of each of said extensionelements, said drive assembly configured and operable to move saidanchor end of said extension elements relative to each other; andon-board electronics associated with said drive assembly and including;an on-board microprocessor connected to said drive assembly and operableto activate said drive assembly to move said one or both of saidextension elements; a power supply providing power to said on-boardmicroprocessor and said drive assembly; a receiver for receivingremotely transmitted data, said receive coupled to said on-boardmicroprocessor to provide said data to said on-board microprocessor,said data including movement data for extending or retracting saidextension element relative to said housing; and at least one sensor forproviding data to said microprocessor indicative of the position and/orforce experienced by the patient's spinal anatomy engaged to said anchorelements, wherein said microprocessor is configured to automaticallycontrol the amount and direction of relative movement of said extensionelements as a function of the sensor data.
 2. The growing rod device ofclaim 1, wherein said at least one sensor includes at least one straingage associated with at least one of said extension elements.
 3. Thegrowing rod device of claim 1, wherein: said at least one sensor isconfigured to determine the Cobb angle of the patient's spine; and saidmicroprocessor is configured to control the relative movement of saidextension elements to achieve a predetermined Cobb angle.
 4. The growingrod device of claim 1, further comprising a housing containing saiddrive assembly and said microprocessor.
 5. The growing rod device ofclaim 1, further comprising a locking device operable to preventrelative movement of said extension elements.
 6. The growing rod deviceof claim 1, wherein said power supply is an inductive power supplyconfigured to inductively receive energy from an external power source.7. The growing rod device of claim 8, wherein said external power sourceis incorporated into a handheld unit.
 8. The growing rod device of claim1, wherein said anchor element includes a slotted plate configured forengagement to the patient's anatomy with a bolt or screw.
 9. The growingrod device of claim 1, further comprising a handheld unit providing aninterface between said on-board microprocessor and a caregiver, saidhandheld unit including means for communicating data to said on-boardmicroprocessor indicative of a desired relative movement of saidextension elements.
 10. The growing rod device of claim 9, wherein: saidhandheld unit includes; a numeric keypad for caregiver entry of adesired movement data; and a transmitter for transmitting said data tosaid receiver; and software resident within said handheld unit and/orsaid on-board microprocessor for translating said movement data intomovement commands for controlling said drive assembly.
 11. The growingrod device of claim 1, wherein said microprocessor is configured toexecute software operable to produce controlled relative movement ofsaid two extension elements to minimize the strain measured by said atleast one strain gage.
 12. The growing rod device of claim 1, whereinsaid on-board microprocessor is configured to execute software adaptedto automatically activate said drive assembly at a predetermined time.13. The growing rod device of claim 1, wherein: said at least one sensorincludes a sensor to adapted to evaluate the physical position of thepatient; and said on-board microprocessor is configured to only activatesaid drive assembly only when the patient is in a predeterminedposition.